Junko Kimura/Getty Images(WASHINGTON) -- President Obama nominated former senator Chuck Hagel to be his next Secretary of Defense on Monday.

Obama on Monday also named counterterrorism advisor John Brennan as the new CIA director to replace David Petraeus, rounding out an overhaul of his national security team.

Hagel, 66, is a decorated Vietnam veteran and businessman who served in the senate from 1997 to 2009. After having sat on that chamber’s Foreign Relations and Intelligence Committees, he has in recent years gathered praise from current and former diplomats for his work on Obama’s Intelligence Advisory Board as well as the policy board of the current Defense Secretary Leon Panetta.

But the former lawmaker faces an upscale battle in the coming confirmation hearings in Congress. Critics on both sides of the aisle have taken aim at his record toward Israel and what some have called a lack of experience necessary to lead the sprawling Pentagon bureaucracy or its operations.

Progressives have also expressed concern about comments he made in 1998, questioning whether an “openly, aggressively gay” James Hormel could be nominated to an ambassador position by then-President Clinton. Hagel apologized for the comments last month, adding that he also supported gays in the military -- a position he once opposed.

The friction with his former colleagues has left a degree of uncertainty in the air going into the hearings. Sunday on ABC’s This Week, Senate Republican Leader Mitch McConnell demurred when asked whether he would support the man who, in 2008, he had championed for his candidness and stature in foreign policy.

“I’m going to wait and see how the hearings go and see whether Chuck’s views square with the job he would be nominated to do,” McConnell told George Stephanopoulos.

Sen. Lindsey Graham was more blunt in his opposition to Hagel on CNN. The Georgia Republican called Hagel an “in your face nomination,” and said he “would be the most antagonistic secretary of defense towards the state of Israel in our nation’s history.”

If confirmed, Hagel will join a crop of new cabinet members expected to join the president in his second term, including Sen. John Kerry, D-Mass., who was nominated in December to replace Hillary Clinton as Secretary of State.